The invention relates generally to the manufacture of electronic devices. More specifically, this invention relates to methods of trimming photoresist patterns and to photoresist pattern trimming compositions useful in the formation of fine lithographic patterns.
In the semiconductor manufacturing industry, photoresist materials are used for transferring an image to one or more underlying layers, such as metal, semiconductor and dielectric layers, disposed on a semiconductor substrate, as well as to the substrate itself. To increase the integration density of semiconductor devices and allow for the formation of structures having dimensions in the nanometer range, photoresists and photolithography processing tools having high-resolution capabilities have been and continue to be developed.
Positive-tone chemically amplified photoresists are conventionally used for high-resolution processing. Such resists typically employ a resin having acid-labile leaving groups and a photoacid generator. Patternwise exposure to activating radiation through a photomask causes the acid generator to form an acid which, during post-exposure baking, causes cleavage of the acid-labile groups in exposed regions of the resin. This creates a difference in solubility characteristics between exposed and unexposed regions of the resist in an aqueous alkaline developer solution. In a positive tone development (PTD) process, exposed regions of the resist are soluble in the aqueous alkaline developer and are removed from the substrate surface, whereas unexposed regions, which are insoluble in the developer, remain after development to form a positive image.
Lithographic scaling has conventionally been achieved by increasing the numerical aperture of the optical exposure equipment and using shorter exposure wavelengths. To form finer photoresist patterns than attainable by direct imaging alone, photoresist pattern trimming processes have been proposed, for example, in US2014/0186772A1. Photoresist trimming processes typically involve contacting a photoresist pattern that includes a polymer having acid labile groups with a composition containing an acid or thermal acid generator. The acid or generated acid causes deprotection in a surface region of the resist pattern, which region is then removed, for example, by contact with a developer solution. The features of the resulting resist pattern are thereby reduced in size as compared with the original resist pattern.
At present, ArF (193 nm) lithography is the standard for mass production of advanced semiconductor devices. ArF photoresist polymers are typically based on (meth)acrylate chemistry and are free or substantially free of aromatic groups in the polymer due to their high absorption at the exposure wavelength. To form finer device geometries than possible with ArF lithography, EUV lithography methods and materials have been and continue to be developed for next-generation devices. An advantage of this technology is the lack of absorption of EUV radiation by aromatic groups, thereby opening up the possibility for use of photoresist material platforms not practical for ArF lithography, for example, vinyl aromatic-based polymers such as polyhydroxystyrene-based polymers. Such materials can be beneficial, for example, from the standpoint of one or more of etch resistance, etch selectivity, sensitivity and cost. However, the use of ArF-resist pattern trimming products with aromatic-based photoresist polymer systems has been found to result in poor patterning performance.
There is a need in the art for photoresist pattern trimming methods and compositions useful in electronic device fabrication that address one or more problems associated with the state of the art.